drivers/net/dummy.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* dummy.c: a dummy net driver
   3
   4         The purpose of this driver is to provide a device to point a
   5         route through, but not to actually transmit packets.
   6
   7         Why?  If you have a machine whose only connection is an occasional
   8         PPP/SLIP/PLIP link, you can only connect to your own hostname
   9         when the link is up.  Otherwise you have to use localhost.
  10         This isn't very consistent.
  11
  12         One solution is to set up a dummy link using PPP/SLIP/PLIP,
  13         but this seems (to me) too much overhead for too little gain.
  14         This driver provides a small alternative. Thus you can do
  15
  16         [when not running slip]
  17                 ifconfig dummy slip.addr.ess.here up
  18         [to go to slip]
  19                 ifconfig dummy down
  20                 dip whatever
  21
  22         This was written by looking at Donald Becker's skeleton driver
  23         and the loopback driver.  I then threw away anything that didn't
  24         apply!  Thanks to Alan Cox for the key clue on what to do with
  25         misguided packets.
  26
  27                         Nick Holloway, 27th May 1994
  28         [I tweaked this explanation a little but that's all]
  29                         Alan Cox, 30th May 1994
  30 */
  31
  32 #include <linux/module.h>
  33 #include <linux/kernel.h>
  34 #include <linux/netdevice.h>
  35 #include <linux/etherdevice.h>
  36 #include <linux/ethtool.h>
  37 #include <linux/init.h>
  38 #include <linux/moduleparam.h>
  39 #include <linux/rtnetlink.h>
  40 #include <linux/net_tstamp.h>
  41 #include <net/rtnetlink.h>
  42 #include <linux/u64_stats_sync.h>
  43
  44 #define DRV_NAME        "dummy"
  45
  46 static int numdummies = 1;
  47
  48 /* fake multicast ability */
  49 static void set_multicast_list(struct net_device *dev)
  50 {
  51 }
  52
  53 static void dummy_get_stats64(struct net_device *dev,
  54                               struct rtnl_link_stats64 *stats)
  55 {
  56         dev_lstats_read(dev, &stats->tx_packets, &stats->tx_bytes);
  57 }
  58
  59 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  60 {
  61         dev_lstats_add(dev, skb->len);
  62
  63         skb_tx_timestamp(skb);
  64         dev_kfree_skb(skb);
  65         return NETDEV_TX_OK;
  66 }
  67
  68 static int dummy_dev_init(struct net_device *dev)
  69 {
  70         dev->pcpu_stat_type = NETDEV_PCPU_STAT_LSTATS;
  71
  72         netdev_lockdep_set_classes(dev);
  73         return 0;
  74 }
  75
  76 static int dummy_change_carrier(struct net_device *dev, bool new_carrier)
  77 {
  78         if (new_carrier)
  79                 netif_carrier_on(dev);
  80         else
  81                 netif_carrier_off(dev);
  82         return 0;
  83 }
  84
  85 static const struct net_device_ops dummy_netdev_ops = {
  86         .ndo_init               = dummy_dev_init,
  87         .ndo_start_xmit         = dummy_xmit,
  88         .ndo_validate_addr      = eth_validate_addr,
  89         .ndo_set_rx_mode        = set_multicast_list,
  90         .ndo_set_mac_address    = eth_mac_addr,
  91         .ndo_get_stats64        = dummy_get_stats64,
  92         .ndo_change_carrier     = dummy_change_carrier,
  93 };
  94
  95 static const struct ethtool_ops dummy_ethtool_ops = {
  96         .get_ts_info            = ethtool_op_get_ts_info,
  97 };
  98
  99 static void dummy_setup(struct net_device *dev)
 100 {
 101         ether_setup(dev);
 102
 103         /* Initialize the device structure. */
 104         dev->netdev_ops = &dummy_netdev_ops;
 105         dev->ethtool_ops = &dummy_ethtool_ops;
 106         dev->needs_free_netdev = true;
 107
 108         /* Fill in device structure with ethernet-generic values. */
 109         dev->flags |= IFF_NOARP;
 110         dev->flags &= ~IFF_MULTICAST;
 111         dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
 112         dev->lltx = true;
 113         dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST;
 114         dev->features   |= NETIF_F_GSO_SOFTWARE;
 115         dev->features   |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA;
 116         dev->features   |= NETIF_F_GSO_ENCAP_ALL;
 117         dev->hw_features |= dev->features;
 118         dev->hw_enc_features |= dev->features;
 119         eth_hw_addr_random(dev);
 120
 121         dev->min_mtu = 0;
 122         dev->max_mtu = 0;
 123 }
 124
 125 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[],
 126                           struct netlink_ext_ack *extack)
 127 {
 128         if (tb[IFLA_ADDRESS]) {
 129                 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
 130                         return -EINVAL;
 131                 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
 132                         return -EADDRNOTAVAIL;
 133         }
 134         return 0;
 135 }
 136
 137 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
 138         .kind           = DRV_NAME,
 139         .setup          = dummy_setup,
 140         .validate       = dummy_validate,
 141 };
 142
 143 /* Number of dummy devices to be set up by this module. */
 144 module_param(numdummies, int, 0);
 145 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 146
 147 static int __init dummy_init_one(void)
 148 {
 149         struct net_device *dev_dummy;
 150         int err;
 151
 152         dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup);
 153         if (!dev_dummy)
 154                 return -ENOMEM;
 155
 156         dev_dummy->rtnl_link_ops = &dummy_link_ops;
 157         err = register_netdevice(dev_dummy);
 158         if (err < 0)
 159                 goto err;
 160         return 0;
 161
 162 err:
 163         free_netdev(dev_dummy);
 164         return err;
 165 }
 166
 167 static int __init dummy_init_module(void)
 168 {
 169         int i, err = 0;
 170
 171         err = rtnl_link_register(&dummy_link_ops);
 172         if (err < 0)
 173                 return err;
 174
 175         rtnl_net_lock(&init_net);
 176
 177         for (i = 0; i < numdummies && !err; i++) {
 178                 err = dummy_init_one();
 179                 cond_resched();
 180         }
 181
 182         rtnl_net_unlock(&init_net);
 183
 184         if (err < 0)
 185                 rtnl_link_unregister(&dummy_link_ops);
 186
 187         return err;
 188 }
 189
 190 static void __exit dummy_cleanup_module(void)
 191 {
 192         rtnl_link_unregister(&dummy_link_ops);
 193 }
 194
 195 module_init(dummy_init_module);
 196 module_exit(dummy_cleanup_module);
 197 MODULE_LICENSE("GPL");
 198 MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it");
 199 MODULE_ALIAS_RTNL_LINK(DRV_NAME);